1. Field of the Invention
The present invention relates to embroidering machines, and more particularly to pattern controlled fabric shifting embroidering machines, having a group of selectively operable needles for color or yarn selection in each of a number of embroidering stations.
2. Description of the Prior Art
Embroidering machines having a group of selectively operable needles in each of a number of embroidering stations, for the selective working of yarns of different color, or yarns of different materials, are known from the prior art. Such an embroidering machine normally has a number of embroidering stations which are regularly spaced across the width of the embroidering machine and in which identical embroidery designs are produced on a fabric which advances under the row of embroidering stations while executing pattern movements.
A needle bar, extending over the length of the machine, carries identical groups of needles in alignment with the embroidering stations, only one needle of each group being operated by the needle bar, while the other needles of the group are immobilized, each holding a different thread, ready to be switched into operation. A complex mechanism is required for the purpose of simultaneously executing identical needle switchover maneuvers in all needle groups.
In a known embroidering machine of this type, disclosed in U.S. Pat. No. 3,884,165, each needle group consists of a certain number of needle rods which carry the embroidering needles and which hold each a different thread. A selector mechanism, designed to operate only one of the needles out of each needle group, features a drive shaft extending across the machine and carrying a drive lever for each needle group. The reciprocating motion of the drive lever is transmitted to the selected needle rod in a two-way positive engagement between the drive arm and the needle rod. In order to switch from one needle rod in the group to another, the drive shaft has to come to a stop in a position in which the needle rods are aligned. This requirement reflects itself in a complex selector mechanism and it is detrimental to the productivity of the machine, due to the need to stop the drive shaft movement.
In another prior art machine of this type, disclosed in U.S. Pat. No. 3,338,194, the switchover is accomplished pneumatically, the needle rods taking the form of small pneumatic cylinders, relative to which the needles are longitudinally adjustable, taking the place of piston rods which protrude from the cylinder-type needle rods. The latter are fixedly attached to the needle bar which executes the stitching motion. An appropriate selector valve energizes the selected needle rod, thereby extending the needle, while all other needles remain retracted, being held by a spring. Though all needles execute the reciprocating motion of the needle bar, only the extended needles reach far enough to produce embroidery stitches.
This prior art solution is complex, inasmuch as it requires a great number of small pneumatic cylinders, with an equal number of separate air supply lines. Furthermore, the needles are poorly guided in their extended position. These needles have a tendency to bind in the extended position, if they are accidentally distorted from the true straight shape.